This invention relates to a telegraphic communication system with automatic handling of connection irregularities in the transmission-reception line of a telegraphic station, the line normally carrying a predetermined current, comprising a polarity detector connected in series with the line to detect the polarity of the circulating current, and a device for reversing the connection of the line.
There are two commonly used line circuits which normally carry an idling current. One is a unipolar circuit providing a single current loop for transmission and reception and which is called a single current system herein. The other is a bipolar circuit with separate current loops for transmission and reception and which is called a double current system herein.
In known single current teleprinter systems, any absence of the idling current for a certain time, followed by a current which is the reverse of the idling current, is interpreted as an erroneous line connection following maintenance work on the line. This situation is detected by a circuit in the teleprinter which after a predetermined time period automatically switches over the polarity of the line connections, in order to re-establish the correct direction of current circulation.
If the line reversal is carried out very rapidly, for example by switching a pin in the exchange, the circuit in question is unable to discriminate the polarity reversal.